The class of foams known as low density, rigid to semi-rigid polyurethane or polyisocyanurate foams has utility in a wide variety of insulation applications, including roofing systems, building panels, building envelope insulation, spray applied foams, one and two component froth foams, insulation for refrigerators and freezers, and so called integral skin foam for cushioning and safety application such as steering wheels and other automotive or aerospace cabin parts, shoe soles, and amusement park restraints. An important factor in the large-scale commercial success of many rigid to semi-rigid polyurethane foams has been the ability of such foams to provide a good balance of properties. In general, rigid polyurethane and polyisocyanurate foams should provide outstanding thermal insulation, excellent fire resistance properties, and superior structural properties at reasonably low densities.
As is known, blowing agents are used to form the cellular structure required for such foams. It has been common to use liquid fluorocarbon blowing agents because of their ease of use, among other factors. Fluorocarbons not only act as blowing agents by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are generally the major contributor to the thermal conductivity properties of the rigid urethane foams. After the foam is formed, the k-factor associated with the foam produced provides a measure of the ability of the foam to resist the transfer of heat through the foam material. As the k-factor decreases, this is an indication that the material is more resistant to heat transfer and therefore a better foam for insulation purposes. Thus, materials that produce lower k-factor foams are generally desirable and advantageous.
In addition to the important performance characteristics mentioned above, it has become increasingly important for the blowing agent(s) used in foamable compositions to have low global warming potential.